When using the calender on my 3rd. Generation Ipad, January and February are fine but when I look for March the screen goes back to wallpaper. !Will I lose any Data if I use the reset.

You don't need to do a reset. Try removing any all-day events from the calendar for the 1st April 2013 e.g. if you are syncing the calendar from somewhere else (e.g. Outlook on a PC or iCal/Calendar on a Mac) then change it to a timed event instead of all-day (if you don't sync your calendar from anywhere then try going into list view, go to 1st April and change any 'all day' events to times e.g. change Easter Monday to start at something like 4am) - it seems that there is a problem with all day events on that date which is when the clocks change due to daylight saving on the day before.

Resetting by holding the power and home buttons at the same time until you see the Apple logo, then releasing will not risk losing any data. However, you might want to try force-closing the Calendar app first as follows: from the home screen, double-tap the home button, locate Calendar in the list at the bottom, tap and hold it until it wiggles, tap ➖ to close it, tap the home button again. Then open Calendar and see if this helped.

Thanks, had same problem created, as you pointed out, by setting 1st April as an all-day event Bank Holiday.